1. Technical
The invention relates to a corrosion-resistant alloy which shows high resistance to stress corrosion cracking even after being subjected to thermal processes such as welding without need for solution treatment thereafter.
2. Prior Arts
Hitherto, a Ni-base alloy containing 26-30% Mo has been generally used for fabricating structural members of reactor vessels, heat exchangers, chemical containers or the like used in chemical plants which are exposed to corrosive atmospheres containing reductive gas such as hydrofluoric gas, gaseous chloric acid or the like, or to non-oxidizing acids such as hydrochloric acid, sulfuric acid, phosphoric acid or the like, the Ni-base alloy showing high corrosion resistance to those corrosive atmospheres and non-oxidizing acids.
This corrosion-resistant Ni-base alloy of the prior art shows excellent properties in cold-working and welding as well as high corrosion resistance to corrosive atmospheres as mentioned above.
However, as can be understood from the binary phase diagram of a Ni-Mo group alloy, this corrosion-resistant Ni-base alloy of the prior art precipitates an inter-metallic compound of Ni.sub.4 MO at temperatures of 600.degree.-800.degree. C. Since this inter-metallic compound causes a reduction of mechanical strength and ductility and the generation of stress corrosion cracking, the alloy of the prior art is normally applied after a solution treatment.
Therefore, even when the corrosion-resistant Ni-base alloy of the prior art is subjected to thermal process such as welding, the alloy is processed through a solution treatment to solve and dissipate the inter-metallic compound precipitated by the welding operation.
However, since the solution treatment to structural members after assembly by welding is limited due to structural and space restrictions and also due to the materials of the welded members, the area of application of the corrosion-resistive Ni-base alloy of the prior art has been limited to date.